This invention relates to an apparatus and method for changing the effective nozzle exit area of a turbofan engine.
A turbofan engine includes a core nacelle housing one or more spools that support at least one compressor and turbine section. One of the spools is used to rotationally drive a turbofan arranged upstream from the core nacelle. A fan nacelle surrounds the turbofan and the core nacelle. The core nacelle is supported by several bifurcations to centrally locate the core nacelle relative to the fan nacelle. In addition to supporting the core nacelle, the bifurcations are used to house various components, such as bleed air conduits and wires, for example. The bifurcations are typically fixed, closed structures.
A generally annular bypass flow path is arranged between the core and fan nacelles through which bypass air from the turbofan flows. The bifurcations are arranged in the bypass flow path. The bypass flow exits from a nozzle exit area at the rear of the engine. The nozzle exit area is typically fixed in a turbofan engine.
It may be desirable in some applications to change the nozzle exit area to control the engine's efficiency and operation. In some military engines, the nozzle exit area is changed by manipulating flaps around its outer perimeter to vary the physical area of the nozzle. Features used to adjust the physical nozzle exit area add significant weight and cost to the turbofan engine, which is particularly undesirable in commercial applications.
What is needed is an apparatus and method to change the effective nozzle exit area while taking advantage of the turbofan engine's existing structure to avoid additional cost and weight.